Feature: Collapsible fields

[Meldiron]

Adds ability to configure a field collapsed:

Example configuration:

content:
  - name: database
    label: Database
    path: database.json
    type: file
    fields:
      - name: users
        label: Users
        type: object
        list: true
        collapsible:
          label: "User {name} ({age} years old)"
          expanded: true
        fields:
         - name: name
           type: string
         - name: age
           type: number

More examples:

        collapsible: true

        collapsible:
          expanded: true

        collapsible:
          label: "User {name} ({age} years old)"

Left to do:

• Address todos
• Confirm approach with maintainer
• Approving review
• Update docs (pages-cms/website)

[hunvreus]

Will merge along with the upcoming blocks release.

[hunvreus]

I would suggest you to have a look at the current version I've pushed to dev and try to rework it for it.

[hunvreus]

I had to rewrite it entirely as there were gaps, conflicts with the latest dev branch and some unaddressed requirements (including some refactoring, e.g. moving object rendering to its own component).

It's partially implemented in 03a722e, I still need to add the support for blocks (but pretty straightforward).

Closing as it will be shipped by tomorrow, but thanks a lot @Meldiron for taking a stab at it. Happy to walk you through my code and discuss why I implemented things differently if that's of interest to you.